The parent patent application describes the use of a free-space photonics switch which takes light projected from the ends of a bundle of optical fibers, operates on the light to perform desired switching functions, and then projects the light into the end of a second array of optical fibers. The optical fiber ends of each bundle form a matrix configuration which must be accurately registered with the other apparatus. Each fiber comprises a core of relatively high index glass having a small diameter, typically five microns, surrounded by low refractive index cladding glass. By holding the ends of the fibers in a securing member having apertures made by photolithogaphic masking and etching, the application describes how the fiber ends can be held in a desired matrix array to within micron tolerances.
Free-space photonic switches also require a matrix aitay of microlenses which must be accurately aligned with the optical fiber ends so that each microlens can focus light onto each fiber end or project light from a fiber end. The paper, "Technique for Monolithic Fabrication of Microlens Arrays," Z. D. Popovic et al., Applied Optics, Vol. 27, No. 7, Apr. 1, 1988, pp. 1281-1284, describes one method of making an appropriate matrix array of microlenses that can be used in conjunction with an optical fiber bundle. The method involves the use of photolithographic masking and etching to form a matrix pattern of polymer elements on a glass substrate. The polymer elements are then heated sufficiently to soften or melt them, giving rise to a roughly spherical meniscus for each element which defines its geometry. The array is then cooled so that the polymer elements are each hardened in a spherical configuration which, in conjunction with the glass substrate, can act as a microlens for focusing light on the core of a single optical fiber. Each microlens is typically twenty-five to two hundred microns in diameter. After the microlens array has been made, properly mounting it in registration with the ends of the optical fiber bundle can be difficult and painstaking.
Because of their importance both to communications and to high-speed computing, there has been a long-felt need in the industry for techniques that can be used to assemble and arrange an array of microlenses with respect to other optical apparatus, that are relatively inexpensive, that do not require a great deal of operator skill, and that are dependably accurate to within micron dimensions.